Browsing by Author "Millet, Guillaume Y."

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    Determining the Maximal Physiological Steady State in Cycling with Precision: Critical Power Estimations or Self-selected Exercise Intensity?
    (2016) Mattioni Maturana, Felipe; Murias, Juan M.; Millet, Guillaume Y.; Paterson, Donald H; MacIntosh, Brian; Passfield, Louis
    Giving the inherent limitations of critical power (CP) testing and the demanding maximal lactate steady state (MLSS) protocol, this thesis aimed: i) to compare the power outputs (POs) derived from two methods of estimating CP (i.e., the power-time relationship (CPHYP) and the 3-minute all-out test (CP3MIN)) and the determined MLSS; and ii) to test cyclists’ ability to predict their highest sustainable PO (CPSELF). Thirteen healthy young participants (26±3 yr; 69.0±9.2 kg; 174±10 cm; 60.4±5.9 mL·kg-1·min-1) were tested. PO at MLSS was lower than CPHYP and CP3MIN (p<0.05). PO at CPSELF was similar (p>0.05) to MLSS. The mean difference between the measures of MLSS and CPSELF was zero, and both methods presented similar (p>0.05) metabolic responses. The disagreement between CPHYP and CP3MIN with the PO at MLSS questions the ability of CP to estimate the maximal steady state, while CPSELF may offer an alternative approach to predict it with more precision.
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    Does the plateau in the NIRS-derived [HHb] signal in the vastus lateralis represent the upper limit in O2 extraction during ramp incremental cycling?
    (2018-09-10) Inglis, Erin Calaine; Murias, Juan M.; Millet, Guillaume Y.; Passfield, Louis
    Oxygen (O2) extraction and O2 delivery represent the two critical components for muscle metabolism and have been extensively studied. The near-infrared spectroscopy (NIRS) derived O2 extraction signal ([HHb]) has been widely used for characterizing the peripheral response to exercise. Research examining this signal in response to ramp-incremental cycling has identified a linear increase followed by a plateau ([HHb]PLATEAU) prior to the achievement of maximal oxygen uptake (V̇O2max). Despite the common occurrence of this plateau, beyond speculation no research has been conducted to examine the underlying mechanisms causing the plateau in this signal. The studies in this thesis contribute to the understanding of the mechanisms that mediate the [HHb]PLATEAU by examining the maximal achievable level of O2 extraction at the end of a ramp-incremental test in different populations. In this two-part study 26 subjects were tested and divided into groups based on sex and training status. The results from the first part of this study demonstrated the existence of a reserve in O2 extraction and suggest that the [HHb]PLATEAU does not represent the upper limit of extraction in the vastus lateralis muscle. Additionally, the second part of this study revealed that sex and training status do not influence the amplitude of the reserve.
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    The Effect of Radiation Therapy and a 12-week Novel Strength Training Intervention on Neuromuscular Function and Fatigability in People Diagnosed with Head & Neck Cancer
    (2019-09-13) Lavigne, Colin; Millet, Guillaume Y.; Culos-Reed, Susan Nicole; Francis, George J.; Lau, Harold Yeehau; Lønbro, Simon
    Treatment for head and neck cancer (HNC) is associated with multiple side-effects and deleterious consequences including reductions in body mass, physical function and health- related quality of life (HRQL). Little is understood about alterations in neuromuscular function and fatigability induced by radiation therapy (RTx). Early evidence suggests strength training is beneficial following treatment for HNC. We hypothesized that exercise prescription could be optimized to promote improvements in muscle strength and mass. This work aimed to investigate the impact of RTx ± chemotherapy on muscle strength, muscle cross-sectional area (CSA) and patient-reported outcomes, and central and peripheral alterations during a whole-body exercise task. Also, we aimed to investigate the feasibility of a 12-week strength training program with the intention of optimizing muscle strength and muscle mass. In the first study, volunteers (n = 10) attended the laboratory before (5 ± 5 days) and after (56 ± 30 days) the completion of anti-cancer treatment. Participants performed a neuromuscular assessment (involving maximal isometric voluntary contractions [MIVC] in the knee extensors and electrical stimulation of the femoral nerve) before and during intermittent cycling to volitional exhaustion. Anthropometrics, self-reported fatigue and HRQL were also assessed. From before to after treatment, MIVC, potentiated twitch, and muscle CSA decreased approximately 18%, 16%, and 20%, respectively. Time to volitional exhaustion was also reduced, and peripheral processes contributed to a reduction in maximal force due to cycling exercise. In the second study, participants (n = 22) were randomized to either an experimental (EXP) strength training intervention involving eccentric overloading and neuromuscular electrical stimulation (n = 11) or a conventional (CON) strength training intervention (n = 11) similar in overall frequency and repetitions. Feasibility outcomes were quantified as rates of accrual, completion, adherence and compliance. Regardless of allocation, 86% of participants completed the intervention and adherence was 88%. From before to after the interventions, muscle strength and muscle CSA in the knee extensors increased ~22% and 18%, respectively. Patient-reported fatigue severity and HRAL also demonstrated clinically relevant improvements. The results of this work suggest that muscle strength and muscle CSA are reduced following treatment for HNC but are regained to a similar extent after 12-weeks of strength training. Also, peripheral fatigue, rather than central fatigue is more pronounced in people affected by HNC following a maximal effort cycling task. Fully supervised strength training programs in survivors of HNC are feasible. These findings offer greater flexibility for future training programs where conventional strength training may not be tolerable.
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    Effects of Fatigue on Neuromuscular Function and Mechanical Properties in Young and Elderly Populations
    (2019-08-20) Lopes Krüger, Renata; Millet, Guillaume Y.; Samozino, Pierre; Edwards, William Brent; Murias, Juan M.; Bilodeau, Martin; Kent-Braun, Jane A.; Aboodarda, Saied Jalal
    Neuromuscular (NM) fatigue is defined as an exercise-related decrease in maximal power or isometric force. However, in the past 20 years, most studies have assessed isometric force only. The evaluation of dynamic measures provides important additional information to the fatigue-induced changes in NM function, especially when exploring age-related changes in fatigability. The few studies that explored dynamic measures of NM fatigue have assessed power output during single-joint movements. Therefore, measures of force production capacity (maximal power, velocity and torque) during multi-joint lower limb movements are unknown. The purpose of this thesis was to examine the effects of different intensities/durations of cycling exercises on torque-velocity properties and NM function in aging and young populations. The specific objectives were: (i) to assess kinetics of central and peripheral fatigue and recovery immediately after different cycling exercises in young individuals; (ii) to compare dynamic vs. isometric measures of NM fatigue following cycling and during recovery in young individuals; and (iii) to explore age-related differences in dynamic and isometric measures (including central and peripheral components of fatigue) of NM fatigue induced by cycling. Thanks to an innovative ergometer, NM fatigue was assessed with a minimal delay (10 s) through dynamic measures of force production capacity during 7-s cycling sprints and maximal isometric force. Our findings showed that: (i) NM fatigue is indeed determined by the exercise intensity/duration and previous studies that investigated NM fatigue with a delay (~ 3 min) might have misinterpreted fatigue amplitude and etiology as well as the course of recovery; (ii) isometric and dynamic measures behave differently after fatigue and so they are not interchangeable as they do not share the same physiological mechanisms; and (iii) younger individuals are as fatigable (for the Wingate and moderate-intensity exercise) or more fatigable (for severe-intensity exercise) than older subjects when considering isometric and dynamic measurements of NM fatigue and peripheral fatigue is greater in younger individuals after the severe- and moderate-intensity exercises, but not following the Wingate. This thesis provides the first comprehensive evaluation of age-related NM fatigue due to dynamic exercises with large muscle mass, i.e. exercises often performed in daily-life and rehabilitation activities.
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    Exercising horses on water treadmills: Understanding the workload, mechanics, and conditioning effects of water treadmill exercise.
    (2019-10-22) McCrae, Persephone; Léguillette, Renaud; Millet, Guillaume Y.; Edwards, William Brent; Rolian, Campbell
    Despite the growing popularity of equine water treadmills (WTs), there is very little scientific evidence to support their use in the conditioning or rehabilitation of sport horses. As a result, the success of WT use is in large part dependent on the ability of the operator to assess and create an appropriate plan. Therefore, the projects described in this thesis were established to assess the workload, conditioning effects, and limb kinetics and kinematics associated with equine WT exercise. The results gathered from these studies will allow more evidence-based use of equine WTs for training and rehabilitation. It was essential to first understand the effort required during WT exercise. We found that water height had a greater impact on workload than the speed of the treadmill belt. The greatest workload occurred with water at the height of the stifle, however this was still considered to be a relatively low-intensity exercise. Using our understanding of workload from the first study, the second study aimed to assess the conditioning effects of a WT exercise program. We assessed the fitness of horses before and after 18-days of WT training, including a dry control (exercised without water), using a maximal intensity exercise track test. Peak oxygen consumption, as tested on the racetrack, increased significantly in the experimental horses, indicating that despite the low workload on the WT, exercising horses in high water heights improves fitness. As the primary rationale for using WTs is to reduce concussive forces experienced by the limb, the third study evaluated the effect of water height and speed on segmental acceleration and impact attenuation during WT exercise. The unique properties of water, especially when water was used at a high level, resulted in reduced segmental accelerations and increased attenuation. These findings suggest that WT exercise may be beneficial in the rehabilitation of lower limb injuries in horses. Lastly, we examined 2-dimensional forelimb kinematics of horses on land and under various WT conditions before and after 8-days of WT conditioning. We found that water height alters limb kinematics and may be meaningful for physical rehabilitation. However, prolonged exposure to WT training does not have a lasting effect overground kinematics. Altogether, these studies have elucidated objective information that will serve as the foundation for the effective and safe use of WTs in the training and rehabilitation of performance horses.
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    Identifying exercise intensity "thresholds": Implications for metabolic responses, performance, and exercise intensity prescription.
    (2019-08-28) Iannetta, Danilo; Murias, Juan M.; Millet, Guillaume Y.; MacIntosh, Brian R.; Paterson, Donald Hugh; Bomhof, Marc R.; Vanhatalo, Anni
    The exercise intensity spectrum, from rest to maximal oxygen uptake (V̇O2max), can be partitioned into three domains of intensity: moderate, heavy, and severe. These domains are demarcated by the lactate threshold (LT) (moderate-to-heavy) and critical power (CP) or maximal lactate steady-state (MLSS) (heavy-to-severe), with the respiratory compensation point (RCP) of the ramp-incremental exercise also being proposed as a marker of the heavy-to-severe boundary of exercise intensity. Although the physiological concepts underpinning these thresholds are well established, methodological issues associated with their determination may lead to inaccuracies and contrasting interpretations regarding their equivalence. The general purpose of this thesis was to find solutions to some of the issues associated with the determination of these “thresholds” and demonstrate why their accurate determination is fundamental in exercise physiology. Using a variety of exercise protocols it was demonstrated that: i) current methods to compute the mean response time (MRT) of V̇O2 during ramp-exercise are inaccurate – the novel method proposed was valid and more reproducible than these methods; ii) exercising slightly above MLSS, although characterized in this study by a stable V̇O2 response, disproportionally impaired maximal exercise capacity; iii) if the V̇O2 dynamics during ramp-incremental exercise are carefully considered, the work rates at RCP and CP/MLSS are not different – refuting the idea that the RCP is not a valid surrogate of the heavy-to-severe boundary of exercise intensity; iv) current methods to prescribe exercise intensity based on fixed-percentage of maximum values (e.g., V̇O2max) do not provide an accurate procedure by which to control exercise intensity. Collectively, these findings provide solutions/explanations to some of the issues related to the correct identification of these exercise thresholds and suggest that their correct identification is of extreme importance when interpreting their physiological implications and to guarantee an accurate exercise intensity prescription.
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    Neuromuscular fatigue of prolonged exercises in normoxia and hypoxia revisited: methodological developments and fatigue etiology
    (2018-07-11) Bartolomeu de Mira, José Miguel; Millet, Guillaume Y.; Rupp, Thomas; Messonnier, Laurent André; Vergès, Samuel; Goodall, Stuart R.; Samozino, Pierre; Deley, Gaëlle; MacIntosh, Brian R.
    The understanding of knee extensor function under fatigue due to whole-body exercise was until recently limited due to short-term recovery. Indeed, subjects needed to be moved from a treadmill/cycle ergometer to an isometric chair, which may underestimate fatigue. This thesis addressed this issue thanks to an innovative ergometer where fatigue can be induced and measured on the same bike, allowing to revisit fatigue etiology in hypoxia and after endurance training. Also, to assess central fatigue, VATMS is traditionally assessed by delivering transcranial magnetic stimulation during three voluntary contractions, each interspersed with 5-10 s of rest (TRADI). In study 1, we assessed whether TRADI methodology resulted in central fatigue underestimation when compared to a continuous approach, with no rest in between voluntary contractions. Post-fatigue, VATMS was heavily underestimated with TRADI. Thus, we propose the continuous method to assess central fatigue. In addition of the lag time explained above, fatigue in hypoxia is poorly understood because of (i) the lack of control in arterial saturation and (ii) different exercise durations in hypoxia vs. normoxia. In study 2, fatigue was assessed on the new cycle ergometer during cycling and right at exhaustion (EXH) in normoxia, moderate and severe hypoxia at relative and absolute workloads. The relative sessions performed in hypoxia were shorter than in normoxia and yet presented lower peripheral fatigue at EXH. This suggests a brain-hypoxic effect that may not only happen in severe hypoxia as previously suggested but also in moderate hypoxia. In study 3, the innovative ergometer was used to revisit the effects of cycling training on neuromuscular fatigue measured during and immediately after cycling exercise. After training, peripheral fatigue was either similar or attenuated at EXH compared to pre-training. The lower or similar fatigue after endurance training suggests that, unlike previously suggested, fatigue may not be upregulated after training.
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    Repeated bout effect and musculoskeletal loading during prolonged downhill running
    (2022-01-19) Khassetarash, Arash; Edwards, W. Brent; Millet, Guillaume Y.; Herzog, Walter; Stefanyshyn,Darren; Aboodarda Saied Jalal
    Running is one of the most common forms of exercise to maintain physical activity and health. Despite decades of research in the field of running biomechanics, the rate of running-related injuries remains high. A vast majority of studies investigating running biomechanics have focused on level running. However, recreational running on urban and rural terrains frequently consists of uphill and downhill running. Owing to high eccentric muscular contraction, downhill running is known to induce muscle damage and symptoms of delayed onset muscle soreness that is generally attenuated during and after a subsequent downhill running bout; a phenomenon known as the repeated bout effect. The primary objective of this thesis was to understand the physiological and biomechanical consequences of an unaccustomed eccentric-biased downhill running bout as well as how the repeated bout effect mediates these consequences. A series of studies were conducted using a model of two prolonged downhill running bouts separated by three weeks. We observed that an unaccustomed downhill run caused substantial neuromuscular fatigue (i.e., central and peripheral fatigue) that persisted up to 48 hours after the initial bout. A repeated bout effect manifested as less sever neuromuscular fatigue following the second downhill run, which was likely due to neural adaptation (i.e., less central fatigue). A repeated bout effect was also observed for downhill running biomechanics, where changes in duty factor and knee quasi-stiffness were attenuated over the course of the second bout compared to the first bout. Changes to bone strain at the lower-extremity over the course of the downhill run were then estimated using combined musculoskeletal-finite element modeling. We observed that the neuromuscular fatigue associated with prolonged downhill running did not impact tibial-fibular strains. The findings from this thesis provide new and important insight to our current understanding of the repeated bout effect in unaccustomed eccentric-biased downhill running as well as the influence of neuromuscular fatigue on bone strain during a prolonged downhill run.
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    The Mechanisms of Fatigability from Whole-Body Exercise and its Relationship to Chronic Fatigue in People with Multiple Sclerosis
    (2018-08-09) Coates, Kyla; Millet, Guillaume Y.; Culos-Reed, Susan Nicole; Zijdewind, Inge; Jarvis, Scott E.
    Objectives: The present study investigated the mechanisms of neuromuscular fatigue in people with Multiple Sclerosis (PwMS) during cycling to determine whether chronic perceived fatigue is associated with motor fatigability in PwMS. Methods: Thirteen PwMS with high levels of perceived fatigue (HF), thirteen PwMS with low levels of perceived fatigue (LF), and thirteen healthy controls (CON) completed an incremental cycling task to volitional exhaustion. By employing an innovative cycle ergometer, neuromuscular evaluations (NME) were performed at baseline, every 3 minutes during cycling, and immediately after exhaustion. Maximal voluntary contractions (MVC) and electrical stimulation of the femoral nerve (PNS) were used to quantify voluntary activation (VA) and muscle contractile ability (PT) of the knee extensors during each NME. The EMG responses to PNS (Mmax) and transcranial magnetic stimulation (MEP) during 50% of MVC were used to quantify central drive (EMG-RMS/Mmax), corticospinal excitability (MEP/Mmax) and corticomotor integrity (MEP latency) in the vastus lateralis (VL) and rectus femoris (RF) muscles during each NME. Results: MVC declined to a greater extent at exhaustion in the HF group compared to the other groups (P = .032) in part due to a larger decline in PT compared to CON (P = .041). EMG-RMS/Mmax in the VL (last commonly completed stage (NME3): P = .047; exhaustion: P = .006), and MEP/Mmax amplitude in the VL (NME3: P = .042; exhaustion: P = .029) and in the RF (NME3: P < .001; exhaustion: P = .007 at exhaustion) were consistently lower in HF compared to CON while MEP latency was consistently longer in HF in the VL (NME3: P = .010; exhaustion: P = .009) and RF (NME3: P = .038; exhaustion: P = .038) compared to CON. Conclusion: Cycling results in greater neuromuscular fatigue at exhaustion in PwMS who experience chronic fatigue than in healthy controls due to central and peripheral alterations.